High-dose, short-term parenteral corticosteroids are in wide use but of unproven value in treating smoke inhalation. It is the purpose of this investigation (1) to determine the LD50 of smoke inhalation for conventional mice, (2) to distinguish the relative contributions of direct injury and superinfection to the pulmonary pathology of smoke inhalation, and (3) to distinguish (if present) the beneficial from infection-promoting properties of corticosteroids used in therapy of smoke inhalation. To accomplish this, mortality, body-weight loss, gross and microscopic pulmonary pathology, and pulmonary bacterial clearance will be studied after administration of an LD50 of sterile smoke to germ-free and conventional mice receiving placebo or corticosteroids after injury.